CH12

CH12

1. Spectroscopy

   • the study of how compounds absorb light which helps us study and analyze chemical compounds.

2. Chemicals

   • Molecules are in constant motion with a constant frequency; they always rotate and vibrate.
   • If a bond in a molecule has the same frequency as the light, then the bond will absorb the light photons
   • The amount of light that can be absorb depends on two things:
     • the number of similar bonds in the molecule
     • the polarity of the bond. Polar molecules will absorb greater than less polar molecule.
       • Bonds of high polarity can cause overtones

3. Light

   • Light is light but there are different versions of light that has different wavelength, frequency, and energy
   • Frequency and energy are proportional
   • Frequency/Energy are inversely proportional
   • Bond vibration and light frequency can have the same frequency

4. Equations

   • Energy = hv
   • v = c/ λ
   • E = h*(c λ) OR E = hcv̄
   • v̄ = 1/ λ
   • f ∝ √(k/ µ)

5. Infrared Region Spectra

   • An IR spectrometer shines light (400-40000 cm-1) through a sample that has molecules in it to measure which W# are absorbed by the molecules. W# that are not absorbed are said to be transmitted which forms the y-axis of an IR spectrum.
   • Regions of IR Spectra
     • <1450 cm-1: is the finger-print region, very difficult to interpret (not in this course!)
     • 1600-1800 cm-1: is the double bond region
     • 2100-2300 cm-1: is the triple bond region
     • >2600 cm-1: is the N-H/O-H/C-H region
   • Types of IR spectra
     • ALKANE
     • ALKENE
     • ALKYNE
     • ALCOHOLS
     • AMINES
     • ALDEHYDES
     • KETONES
     • CARBOXYLIC ACIDS
     • NITRILES
     • ESTERS

6. Effects of Conjugation

   • Delocalization of π bonds will result in a lower wavenumber, lower stretching frequencies. The reason for that because by delocalizing the π bonds the bonds will be less which result in less bond vibration.